The present invention relates to a converging reflector to reflect a light from a light source to converge or condense and project the reflected light onto a predetermined plane of irradiation, and more particularly to a converging reflector capable of improving convergence efficiency and a liquid crystal display device including such a converging reflector.
Conventional converging reflectors of one type are formed by a reflection mirror of paraboloid of revolution (which will be simply referred to as a parabolic reflector hereinafter) wherein a light source is arranged at the focal point of the paraboloid of revolution to reflect a light from the light source to form a parallel light by means of the parabolic reflector.
Further, conventional converging reflectors of another type are formed by a reflecting mirror of ellipsoid of revolution (which will be simply referred to as an elliptic reflector hereinafter), wherein a light source is arranged at a first focal point of the ellipsoid of revolution to allow a light from the light source to converge into a second focal point by means of an elliptic reflector and the reflected light by the reflecting mirror is changed into a parallel light by means of a condenser lens whose focal point is coincident with the second focal point.
In the respective conventional converging reflectors, a point light source is arranged at the focal point of each reflecting mirror to thereby emit rays of parallel light or rays of convergent light, thus permitting those rays of light to be reflected on an ideal circular plane of projection or an ideal point.
Further, conventional liquid crystal display devices are of a structure to separate a white light from the converging reflector into rays of light of three colors of R, G and B by using three dichroic mirrors. Respective rays of color lights of R, G and B are incident on each of liquid crystal cells through a condenser lens to vary transmittance of the liquid crystal cell in dependency upon respective image signals to thereby allow respective rays of incident color lights of R, G and B to be transmitted therethrough or intercepted thereby, thus to project images corresponding thereto onto a screen through a projection lens.
However, since conventional converging reflectors are constructed as described above, a light source which can be considered as a point light source must be arranged at the focal point of the reflecting mirror in order to permit a light to be reflected on an ideal circular plane of projection or an ideal point. When an attempt is made to realize a light source of high luminance or brightness, the light source itself would be large. For example, a metal halide lamp is used as a high luminance one. However, a light is emitted between two electrodes in the metal halide lamp. For this reason, such a light source cannot be considered as a point light source and the size of that light source would not be negligible, thus disadvantageously failing to allow a light to be reflected on a circular plane of projection or a point.
Further, since a metal halide lamp of the double tube type employed as the light source mentioned above is of a structure using a large valve as its outer tube, a light reflected by the reflecting mirror impinges on the valve itself, and is scattered and absorbed, disadvantageously resulting in a lowered convergence efficiency.
In addition, in the case of conventional liquid crystal display devices, although a light from the converging reflector is projected through the dichroic mirrors, the condenser lenses, the liquid crystal cells, and the projection lens, only the convergence efficiency of the converging reflector is taken into consideration, but the correlation of the entirety of the device is not taken into consideration by any means. Thus, the convergence efficiency of the entirety of the device is unable to be improved.